Bard Solid State Dual Unit Lead/Lag Controller MC4000 - Manual (Page 9)

Manual 2100-563C
Page 9 of 40
HUMIDITY CONTROL OPTION
Note: This function is not available if controller is
configured for heat pump.
The standard air conditioning system can be adapted to
perform dehumidification control by addition of a
simple humidity controller that closes-on-rise, and is
connected to terminals H1 and H2 on the main controller
board. Recommended Bard Part #8403-038 (H600A
1014). Both HVAC units must be equipped with electric
heat for this sequence to work properly. See appropriate
connection diagram - Figures 1 - 12 for this connection:
1. Temperature control always has priority over
dehumidification. If there is any stage of cooling
demand active, the dehumidification sequence is
locked out.
2. If all stages of cooling are satisfied, and relative
humidity is above the set point of humidity
controller:
a. The green “Dehumid. Operation” light will come
on, and the lag unit compressor and blower will
operate until the set point of humidity controller
is satisfied (or cancelled by a call for cooling).
b. If the space temperature drops to 67F, the electric
heater of the lead unit will cycle to help maintain
building temperature. It will cycle off at 69F.
c. If space temperature drops to 64F, the Stage 2
Heating light will come on and the lag unit
compressor operating for dehumidification mode
will cycle off until the building temperature rises
above 65F from 1st stage heat and building load.
The green “Dehumid. Operation” light stays on
during this sequence, and when Stage 2 Heating
light is Off, the compressor is On. The electric
heater in lag unit is locked out in
dehumidification mode.
Lag unit outputs G, Y1 and Y2 are all switched on
during dehumidification sequence. This is true for both
alternating and non-alternating controller configurations.
COOLING OPERATING SEQUENCES FOR
ALTERNATING LEAD/LAG/LEAD/LAG
CONFIGURATION
1. 1-Stage Compressor Units No Economizer
1 st stage cooling set point is the setting (SP) input into
the controller. Factory default is 77F (25C). On a call for
cooling the blower of the lead unit will come on
immediately (if not already on – See Blower Operation),
and the Stage 1 LED will blink for 10-seconds before
going solid, at which time the compressor will start.
2 nd cooling set point is 4F (default setting, user
selectable 2-6F) warmer than Stage 1. On a call for 2 nd
Stage cooling the blower of the lag unit is turned on (if
not already on – See Blower Operation), and the Stage 2
LED will blink for 10-seconds before going solid, at
which time the compressor will start.
3 rd and 4 th stages are functional outputs but there is
nothing to be controlled.
2. 2-Stage Compressor Units No Economizer
1 st stage cooling set point is the setting (SP) input into the
controller. Factory default is 77F (25C). On a call for
cooling the blower of the lead unit will come on
immediately (if not already on – See Blower Operation),
and the Stage 1 LED will blink for 10-seconds before
going solid, at which time the lead unit compressor will
start in compressor Stage 1 partial capacity operation.
2 nd cooling set point is 4F (default setting, user selectable
2-6F) warmer than Stage 1. On a call for 2 nd Stage
cooling the blower of the lag unit is turned on (if not
already on – See Blower Operation), and the Stage 2
LED will blink for 10-seconds before going solid, at
which time the lag unit compressor will start in
compressor Stage 1 partial capacity operation.
3 rd cooling set point is 2F (default setting, user selectable
2-3F) warmer than Stage 2. On a call for 3 rd Stage
cooling the Stage 3 LED comes on solid (no delay), and
the lead unit compressor will switch to compressor Stage
2 full capacity operation.
Humidity controller set point should be in 50-60%
relative humidity area: Setting controller to lower
settings will result in excessive operating time and
operating costs for the electric reheat, and in
extreme cases could cause evaporator (indoor) coil
freeze-up if there are periods of light internal
equipment (heat) loading.
CAUTION